There is known a technology of transferring images from a data processing apparatus such as a digital camera to an information processing apparatus such as a PC (personal computer). In order to show data concerning the survey of images stored in a digital camera to a user, there is known a technique of displaying on a PC, in thumbnail format, images stored on the digital camera. For example, Japanese Patent Laid-Open No. 2005-123928 discloses a digital camera which extracts only thumbnail images from stored images and transfers them.
In order for a PC to acquire thumbnail images from a digital camera, it is necessary for the following four steps to be carried out according to a PTP (Picture Transfer Protocol).
(1) The digital camera generates a list containing directory and file information of a storage medium containing stored images. A file refers mainly to an image file, but other file types (e.g., audio files) may be included.
(2) The PC refers to the list and sends a request to the digital camera to transfer the necessary thumbnail images.
(3) The digital camera extracts thumbnail images from image files in response to receiving the transfer request from the PC, and sends the thumbnail images to the PC.
(4) The number of times the above processes (2) and (3) are repeated equals the number of thumbnail images required by the PC.
However, if a PC attempts to acquire a thumbnail image by conventional methods, there arises the problem of large overhead involved in transmission. For example, if 1000 thumbnail images are to be acquired, it is necessary for a PC and a digital camera to repeat the above processes (2) and (3) 1,000 times. This requires a long period of time.
In addition, computing units of a digital camera are often configured to be relatively slow in order to limit power consumption and costs. Consequently, it takes a relatively long time for such a digital camera to extract thumbnail images from image files.
As a result, there is the problem that a long period of time is required for all thumbnail images required by a PC to be extracted and displayed to a user.
Thus, it takes a long period of time for a portable data processing apparatus such as a digital camera to extract specific data from files. Consequently, there is a considerable delay until the data is displayed to a user.
The present invention is provided in view of this situation, and provides a technology for reducing the amount of time required for an information processing apparatus to acquire thumbnail images from a data processing apparatus and display them to a user.